Preparation of photosensitive block copolymer elements

ABSTRACT

Photosensitive elements comprising a layer of a solvent-soluble, thermoplastic, elastomeric, block copolymer, a nongaseous ethylenically unsaturated compound, and an addition polymerization initiator activatable by actinic light interposed between a support and cover sheet, a flexible polymeric film, e.g., polyamide, being interposed between the cover sheet and the surface of the layer. The elements are useful in preparing printing plates, particularly flexographic printing plates, and other relief images.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of application Ser. No. 229,068 filedJan. 28, 1981 now U.S. Pat. No. 4,369,246, which is acontinuation-in-part of Application Ser. No. 160,439, filed June 17,1980, now abandoned, which is a division of Application Ser. No.926,479, filed July 20, 1978, now abandoned, which is acontinuation-in-part of Application Ser. No. 374,567, filed June 28,1973,now abandoned, which is a continuation-in-part of Application Ser.No. 130,470, filed Apr. 1, 1971, now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to photosensitive elastomeric elements having alayer of photosensitive, solvent-soluble, thermoplastic, elastomericcompositions which upon exposure to actinic light formsolvent-insoluble, elastomeric materials, and to a process for makingreliefs from such elements, and still more particularly, to a processfor making flexographic printing reliefs from such elements.

Flexographic printing reliefs which are useful for letterpress printingof packaging materials, e.g., cardboard, plastic films, etc., areconventionally prepared by a laborious procedure involving art work,photographic negative, photoengraving, formation of a phenolic matrix,and hot press molding of a rubber plate. Printing reliefs with resilientsurfaces can be prepared directly from photosensitive compositions asexemplified in assignee's U.S. Pat. Nos., McGraw 3,024,180, granted Mar.6, 1962 and Barney 2,948,611, granted Aug. 9, 1960. In the processesdescribed in said patents, printing reliefs having characters of uniformprinting height are produced by exposing to actinic light through animage-bearing transparency (negative or positive) a layer comprising anaddition-polymerizable, ethylenically unsaturated compound or mixture ofcompounds, a solvent-soluble elastomeric binder, and having dispersedtherethrough an addition-polymerization initiator activatable by saidactinic light, and being superposed on and adherent to a suitablesupport, e.g., a metal plate or foil, until addition polymerization,i.e., insolubilization of the composition occurs in the nonexposedareas. Removal of the layer in the nonexposed areas, e.g., by treatmentwith a suitable solvent in which the polymerized composition in theexposed areas is insoluble, leaves a printing relief of the line orhalftone image of the transparency suitable for letterpress work.Frequently, however, these printing reliefs are not as elastomeric asthe molded rubber plates. Also the photosensitive elements tend to coldflow due to high monomer concentrations needed and do not have thedesirable features of vulcanized rubber without reducing solventsolubility as well. Furthermore, such compositions and elements oftenmust be solvent coated, thus reducing the effective use of the elements.

SUMMARY OF THE INVENTION

An object of this invention is to provide new photosensitive,solvent-soluble elements which are useful in making reliefs, andparticularly flexographic printing reliefs, for letterpress printing.Another object of this invention is to provide such photosensitiveelements which are thermoplastic and elastomeric and resistant to coldflow prior to imagewise exposure. A further object of this invention isto provide such elements which result in flexographic printing reliefsfor use with alcoholic or aqueous inks. A still further object of thisinvention is to provide such elements which result in relief imagesuseful as resists or in planographic printing. Still other objects willbe apparent from the following description of the invention.

The invention includes photosensitive elements which comprise a sheetsupport; a layer of a photosensitive, elastomeric composition coated onsaid support having a thickness of from about 0.0005 to about 0.250inch, said composition comprising

(1) at least 30% by weight of at least one solvent-soluble,thermoplastic, elastomeric block copolymer containing at least twothermoplastic, nonelastomeric polymer blocks having a glass transitiontemperature above 25° C. and an average molecular weight of2000-100,000, and between said thermoplastic, nonelastomeric polymerblocks an elastomeric polymer block having a glass transitiontemperature below 10° C. and an average molecular weight of about 25,000to 1,000,000.

(2) at least 1% by weight of an addition-polymerizable ethylenicallyunsaturated compound containing at least one terminal ethylenical group,and

(3) a polymerization-effective amount of polymerization initiatoractivatable by actinic radiation;

a flexible cover sheet; and a flexible, polymeric film interposedbetween said cover sheet and the surface of said layer.

Polymeric molecular weights referred to herein are number averagemolecular weights (Mn). The number average molecular weights for theblock copolymers, e.g., as specified in the examples, can be determinedby membrane osmometry utilizing a gel cellophane 600 W membranemanufactured by Arro Laboratories, Inc., Joliet, Ill., toluene as thesolvent at 29° C. The Mn for the nonelastomeric polymer blocks andelastomeric polymer blocks are preferably determined as follows:

A. The molecular weight of the first block (polystyrene) can be measuredby gel permeation chromatography (GPC) of a terminated sample removedimmediately after the polymerization. The chromatograph is calibratedusing commercially available polystyrene molecular weight standards.

B. The Mn of the second block (polyisoprene or polybutadiene) can bedetermined in the following manner:

(1) measuring by suitably calibrated GPC the Mn of a sample ofpolystyrene-polyisoprene (or polybutadiene) diblock polymer terminatedand removed immediately after its polymerization, and (2) subtractingfrom this value the Mn of the first block as determined in (A) above.

C. The Mn of the third block (polystyrene) can be determined in the samegeneral manner:

(1) measuring by suitably calibrated GPC the Mn of the sample ofpolystyrene-polyisoprene (or polybutadiene)-polystyrene triblockpolymer, and

(2) subtracting from this value the Mn of the diblock polymer obtainedin (B) above. The block copolymers are manufactured by Shell ChemicalCompany and sold under the trademark "Kraton®".

In another aspect of this invention there is provided a process forforming a solvent-insoluble, elastomeric printing relief comprisingapplying to a sheet support a layer of the photosensitive, elastomericcomposition as described above to a dry thickness of from about 0.0005to about 0.250 inch; laminating a flexible, polymeric film and aflexible cover sheet to said layer, so that the surface of said film iscontiguous to the surface of said layer; stripping said cover sheet fromsaid film; imagewise exposing the photosensitive layer to actinicradiation through said film; and removing said film and the unexposedareas of said layer by solvent-washing.

The photosensitive elements of this invention have the advantage thatthe elastomeric compositions used to form the photosensitive layerspossess certain mechanical properties similar to those of conventionalreinforced rubber vulcanizates, such as high tensile strength and rapidreturn from high extension, as well as certain properties ofconventional thermoplastics, such as a reversible transition to a meltwith a moderate increase in temperature. Such novel features allow theeasy preparation and manipulation of the photosensitive compositionsinto useful elements without affecting solubility in processingsolvents. Furthermore, when elements of this invention are imagewiseexposed to actinic radiation, the exposed areas become insoluble andresult in tough, shaped, elastomeric reliefs with subsequent solventremoval of unexposed portions of the composition. The presence of aflexible, polymeric film interposed between the cover sheet and surfaceof the photosensitive layer, after removal of the cover sheet, providesa hard layer that is easily developed when the exposed areas of theelement are developed. Due to their smooth hardness a surface, e.g.,image-bearing negatives, placed in contact with the element is readilyremoved without sticking to the surface of the element.

This invention provides photosensitive elements for producingflexographic letterpress printing plates of uniform printing height fromrelatively inexpensive materials and with a marked reduction in laborrequirements over the conventional procedure. Both the relief andprinted images obtained show fidelity to the original transparency bothin small details and in overall dimensions even when the element isimagewise exposed on a cylindrical support. The printing reliefs havethe advantage that they have mechanical properties similar toconventional reinforced rubber vulcanizates and do not becomepermanently deformed in normal use. The reliefs have high impactstrength and are not brittle but are tough and abrasion-resistant andhave unusually long press wear using conventional alcohol and waterbased inks. Hardness of the reliefs can be easily changed by varyingcomponent concentrations.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In a preferred aspect of this invention the photosensitive compositionscomprise a solvent-soluble, thermoplastic, elastomeric, A-B-A blockcopolymer, at least one compatible, addition-polymerizable,ethylenically unsaturated compound containing at least one terminalethylenic group, and polymerization-effective amounts, e.g., 0.01 to10%, or more, by weight of the photosensitive composition, of anaddition-polymerization initiator activatable by actinic radiation andinactive thermally below 85° C., a polymerization effective amount beingan amount that is sufficient to effect polymerization. Particularlypreferred addition-polymerization initiators useful in thephotosensitive compositions, are inactive thermally below 185° C. Thephotosensitive composition can also contain a small amount of a thermaladdition-polymerization inhibitor and can also contain compatiblefillers, plasticizers, antioxidants and antiozonants.

In general the ratio by weight of the block copolymer to the compatible,addition-polymerizable, ethylenically unsaturated compound would rangefrom 99:1 to 1:1.

Preferred block copolymers useful in this invention have at least oneunit of the general formula, A-B-A, wherein each A is an independentlyselected nonelastomeric polymer block having an average molecular weightof 2000-100,000 and a glass transition temperature above 25° C. and B isan elastomeric polymer block having an average molecular weight betweenabout 25,000 and 1,000,000 and a glass transition temperature belowabout 10° C. The nonelastomeric blocks, A, having between them anelastomeric block, B, together comprise the unit A-B-A which representsthe copolymers uniquely suitable for use in combination with thephotopolymerizable components in the compositions of the invention. Thisunit may comprise the entire general formula of the copolymer; it may beappended to another polymer chain; or it may be repeating. It is, ofcourse, possible to vary the precise nature of the unit within the scopeof the invention, e.g., by using two different nonelastomeric terminalblocks, A, or by creacting block or graft polymeric substitutions inblocks A and B. Preferably, the elastomeric mid-section blocks, B, arepolymers of aliphatic conjugated diolefins while the nonelastomericblocks, A, are those formed by polymerizing alkenyl aromatichydrocarbons, preferably vinyl substituted aromatic hydrocarbons, andstill more preferably vinyl monocyclic aromatic hydrocarbons. The blockcopolymers are disclosed in Holden et al. U.S. Pat. No. 3,265,765 andcounterpart British Pat. No. 1,000,090, hereby incorporated byreference. Particularly preferred species of the subject copolymerscomprise block copolymers of polystyrene terminal groups connected by amid-section of polyisoprene or polybutadiene, e.g.,polystyrene-polyisoprene-polystyrene orpolystyrene-polybutadiene-polystyrene, the polydiene block being 70 to90% by weight of the block copolymer. Other typical block copolymersuseful in this invention are polystyrene-polybutadiene-polystyrene andpolystyrene-polyisoprene-polystyrene block copolymers which have beenhydrogenated according to the teachings of Jones, U.S. Pat. No.3,431,323 and Hefele et al., U.S. Pat. No. 3,333,024. The hydrogenatedblock copolymers have the additional advantage of improved thermal andoxidative resistance. However, some residual unsaturation inhydrogenated block copolymers is desirable, since only very smallconcentrations of monomer are then needed in the photosensitivecompositions to reduce solvent solubility upon exposure to actinicradiation. Still other typical block-copolymers useful in this inventionare those wherein the terminal blocks are polyalkyl styrenes, e.g.,poly(α-methyl styrene)-polyisoprene-poly (α-methyl styrene), and thosecomposed of a plurality of polymer blocks, e.g.,polyisoprene-polystyrene-polybutadiene-polystyrene-polyisoprene.

Among useful addition-polymerization ethylenically unsaturated compoundswhich form compatible mixtures with the aforesaid thermoplastic,elastomeric block copolymers are:

t-butyl acrylate

N,N-diethylaminoethyl acrylate

1,4-butanediol diacrylate

hexamethylene glycol diacrylate

decamethylene glycol diacrylate

2,2-dimethylolpropane diacrylate

tripropylene glycol diacrylate

trimethylol propane triacrylate

2,2-di(p-hydroxyphenyl)-propane diacrylate

2,2-di(p-hydroxyphenyl)-propane dimethacrylate

polyoxyethyl-2,2-di(p-hydroxyphenyl)-propane dimethacrylate

polyoxypropyltrimethylol propane triacrylate (462)

butylene glycol dimethacrylate

hexamethylene glycol dimethacrylate

2,2,4-trimethyl-1,3-pentanediol dimethacrylate

1-phenyl ethylene-1,2-dimethacrylate

trimethylol propane trimethacrylate

diallyl fumarate

styrene

1,4-diisopropenyl benzene

1,3,5-triisopropenyl benzene

Compounds having one or two ethylenic groups are particularly preferred.

The photosensitive compositions of this invention essentially do notscatter the actinic radiation when in the form of thin layers, e.g.,about 0.0005 to about 0.250 inch. In order to secure an essentiallytransparent mixture, i.e., a nonlight-scattering mixture, thethermoplastic-elastomeric block copolymer component should be compatiblewith and preferably soluble in, the ethylenic component when used withinthe aforementioned ratio range of 99:1 to about 1:1 wherein the ratio isthe weight of block copolymer used to the weight ofaddition-polymerizable, ethylenically unsaturated compound used.

By compatibility is meant the ability of two or more constituents toremain dispersed with one another without causing appreciable scatteringof actinic radiation. Compatibility is often limited by the relativeproportions of the constituents and incompatibility is evidenced byformation of haze in the photosensitive composition. Some slight haze oflayers coated or extruded from such compositions before or duringexposure can be tolerated in the preparation of printing reliefstherefrom but when fine detail is desired, haze is preferably avoided.The amount of monomer, or any other constituent, used is thereforelimited to those compatible concentrations below that which producesundesired light scatter or haze. The above compatible ethylenicallyunsaturated compounds form high-molecular weight addition polymersreadily by photoinitiated addition polymerization in the presence of anaddition polymerization initiator. Of course, the initiator absorbssufficient radiant energy to initiate polymerization or cross-linking.

Practically any initiator of addition polymerization which is capable ofinitiating polymerization under the influence of actinic radiation canbe used in the photosensitive compositions of this invention. Becausetransparencies transmit heat originating from conventional sources ofactinic radiation and since the photosensitive compositions may beusually prepared under conditions resulting in elevated temperatures,the preferred initiators are inactive thermally below 85° C. They shouldbe dispersible in the composition to the extent necessary for initiatingthe desired polymerization or cross-linking under the influence of theamount of radiation absorbed in relatively short term exposures. Theseinitiators are useful in amounts from 0.001 to 10.0%, or more, andpreferably from 0.01% to 5% based on the weight of the photosensitivecomposition.

Suitable photopolymerization initiators include vicinal diketones, e.g.,diacetyl, benzil, α-pyridil, etc.; acyloins, e.g., benzoin, pivaloin,α-pyridoin, acyloin ethers, e.g., benzoin methyl and ethyl ethers;alpha-hydrocarbon-substituted aromatic acyloins, e.g., α-methyl benzoin,α-t-butyl benzoin, acyloin esters, e.g., benzoin acetate, and α-allylbenzoin; substituted and unsubstituted quinones having two intracycliccarbonyl groups attached to intracyclic carbon atoms in a conjugated sixmember carbocyclic ring there being at least one aromatic carbocyclicring fused to the ring containing the carbonyl groups, e.g.,ethyl-anthraquinone, benzanthraquinone, etc., and benzophenone and4,4'-bis(dimethylamino)benzophenone. Initiators can be used separatelyor in conjunction with other coinitiators, e.g., ethylanthraquinone with4,4'-bis(dimethylamino)-benzophenone and benzoin methyl ether withtriphenyl phosphine. Also useful in aspects of this invention areinitiators and initiator systems disclosed in assignees U.S. Pat. Nos.,Chambers, 3,479,185, issued Nov. 18, 1969; Chang et al., 3,549,367,issued Dec. 22, 1970; Fan, 3,558,322, issued Jan. 26, 1971 and Chang,3,661,588, issued May 9, 1972.

The photosensitive compositions may also contain a small amount ofthermal addition polymerization inhibitor, e.g., 0.001% to 2.0% based onthe weight of the photosensitive composition. Suitable inhibitors thatcan be used in addition to the preferred2,6-di-tert-butyl-4-methylphenol and p-methoxyphenol includehydroquinone, and alkyl and aryl-substituted hydroquinones,tert-butyl-pyrocatechol, pyrogallol, naphthylamines, beta-naphthol,2,6-di-tert-butyl-p-cresol, phenothiazone, pyridine, nitrobenzene anddinitrobenzene. Other useful inhibitors include p-toluquinone, chloraniland thiazine dyes, e.g., Thionine Blue G (CI 52025), Methylene Blue B(CI 52015) and Toluidine Blue (CI 52040). Such compositions can bephotopolymerized or photocrosslinked without removal of the inhibitor.

The photosensitive elements of this invention can be made by solventcasting or by extruding, calendering or pressing at an elevatedtemperature of the photosensitive composition into the form of a layeron a suitable casting wheel, belt or platen as a self supporting sheet.The layer or sheet may be laminated to the surface of a suitablepermanent support or, if necessary, it may be affixed by means of asuitable adhesive, or the solution may be coated directly onto asuitable support. The photosensitive elements may have antihalationmaterial beneath the photosensitive layer. For instance, the support maycontain an antihalation material or have a layer or stratum of suchmaterial on its surface. The elements may be made in the various mannersdescribed in Plambeck U.S. Pat. Nos. 2,760,863 and 2,791,504 and McGrawU.S. Pat. No. 3,024,180. The photosensitive layer itself can serve asthe light absorption layer, e.g., when dyes or pigments are included inthe photosensitive composition or when the layer is sufficiently thick.

Suitable base or support materials include metals, e.g., steel andaluminum plates, sheets and foils, and films or plates composed ofvarious film-forming synthetic resins or high polymers, such as theaddition polymers and in particular vinylidene chloride copolymers withvinyl chloride, vinyl acetate, styrene, isobutylene and acrylonitrile;vinyl chloride homopolymers and copolymers with vinyl acetate, styrene,isobutylene and acrylonitrile; linear condensation polymers such aspolyesters, e.g., polyethylene terephthalate, polyamide, e.g.,polyhexamethylenesebacamide; polyimides, e.g., films as disclosed inassignee's Edwards, U.S. Pat. No. 3,179,634 and polyester amide, e.g.,polyhexamethyleneadipamide adipate. Fillers or reinforcing agents can bepresent in the synthetic resin or polymer bases such as the variousfibers (synthetic, modified, or natural), e.g., cellulosic fibers, forinstance, cotton, cellulose acetate, viscose rayon, paper; glass wool;nylon and polyethylene terephthalate. These reinforced bases may be usedin laminated form. Various anchor layers disclosed in U.S. Pat. No.2,760,863 can be used to give strong adherence between the support andthe photosensitive layer or, in the case of transparent support,pre-exposure through the support to actinic radiation may be useful. Theadhesive compositions disclosed in assignee's Burg U.S. Pat. No.3,036,913 are also effective.

Printing reliefs can be made in accordance with this invention byexposing to actinic radiation selected portions of a photosensitivelayer of an element described above, for example, through animage-bearing transparency or stencil having areas essentiallytransparent to actinic radiation and of substantially uniform opticaldensity and areas opaque to actinic radiation and of substantiallyuniform optical density until substantial addition-polymerization orphotocrosslinking takes place, i.e., the radiation-exposed portions ofthe layer are converted to the insoluble state with no significantpolymerization or crosslinking taking place in the unexposed portions orareas of the layer, and removing unexposed portions of the layer bymeans of a solvent for the thermoplastic-elastomeric block copolymer.During the addition-polymerization or crosslinking, insolubilizationoccurs and the thermoplastic-elastomeric block copolymer/ethylenicallyunsaturated compound containing composition is converted to theinsoluble state.

The thickness of the photosensitive layer is a direct function of thethickness desired in the relief image and this will depend on thesubject being reproduced and the ultimate use of the relief, e.g., thicksoft reliefs are useful for flexographic printing and thin hard reliefsare useful for planographic printing. In general, the thickness of thepolymerizable layer will vary from about 0.0005 to about 0.250 inches ormore and layers within this range of thickness will be used for themajority of the printing plates.

The photosensitive layers may also, if desired, include compatibleplasticizers, other unsaturated compounds and polymers. Such agents,preferably superior solvents for the thermoplastic-elastomeric polymer,may be used to improve the rate or extent of insolubilization throughoutthe photosensitive layer, to facilitate the removal of the unexposedareas, and to aid the manufacture of the layers. Useful materials arehydrocarbon oils, e.g., naphthenic and paraffinic oils; polymers andresins, e.g., polystyrene, α-methyl styrene-vinyl toluene copolymers,pentaerythritol ester of hydrogenated rosin, polyterpene resins, esterresins, polyethylene, poly-α-methyl styrene, and polyacrylates; andstearic acid.

The photosensitive layers can also contain immiscible polymeric ornonpolymeric organic or inorganic fillers or reinforcing agents which donot scatter actinic radiation and preferably are substantiallytransparent, e.g., polystyrene, the organophilic silicas, bentonites,silica, powdered glass, zinc stearate, zinc oxide, etc. having aparticle size less than 0.0001 inch and in amounts varying with thedesired properties of the photosensitive layer. Compositions may alsocontain dyes (e.g., indigo) for indentification or aesthetic purposes,provided they do not strongly absorb actinic radiation and do notinterfere with the addition polymerization reaction.

Resistance of photosensitive elements of this invention and printingreliefs made therefrom to oxygen and ozone attack can be improved byincorporating in the photosensitive composition a suitable amount ofcompatible well known antioxidants and/or antiozonants. Antioxidantsuseful in this invention include: alkylated phenols, e.g.,2,6-di-tert-butyl-4-methyl phenol; alkylated bis-phenols, e.g.,2,2-methylene-bis-(4-methyl-6-tert-butyl phenyl);1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl) benzene;2-(4-hydroxy-3,5-tert-butylanilino)-4,6-bis-(n-octylithio)1,3,5-triazone; polymerized trimethyldihydroquinone; zinc dibutyl dithiocarbamate anddilaurylthiodipropionate. Antiozonants useful in this invention include:micro crystalline wax and paraffin wax; dibutyl thiourea;1,1,3,3-tetramethyl-2-thiourea; Antiozonant AFD, a product of NaftonCo.; norbornenes, e.g., di-5-norbornene-2-methyl adipate,di-5-norbornene-2-methyl maleate, di-5-norbornene-2-methylterephthalate, etc.; Ozone Protector 80, a product of Reichhold ChemicalCo.; N-phenyl-2-naphthylamine; unsaturated vegetable oils, e.g.,rapeseed oil, linseed oil, safflower oil, etc.; polymers and resins,e.g., ethylene vinyl acetate copolymer resin, chlorinated polyethylene,chlorosulfonated polyethylene, chlorinated ethylene methacrylic acidcopolymer, polyurethanes, polypentadienes, polybutadiene, furfuralderived resins, ethylene propylene diene rubber, diethylene glycol esterof resin, and α-methyl styrene-vinyl toluene copolymer. Ozone resistanceof the printing relief produced can also be improved by annealing it atelevated temperatures prior to use.

The photosensitive compositions are, in general, solids. They are also,frequently, depending on their composition, somewhat tacky on thesurface. This latter property is of advantage in that compositionsadhere of themselves to a support being used and do not usually requirethe application of an adhesive to retain them on the support, bothduring photo-exposure and development steps and during subsequent use ofthe insolubilized material as a printing plate. A transparent coversheet such as a thin film of polystyrene, polyethylene, polypropylene orother strippable material is used to prevent contamination of or damageto the photosensitve layer during storage or manipulation. A thin hard,flexible, solvent-soluble layer, e.g., a layer of a polyamide, copolymerof ethylene and vinyl acetate, etc., is used on the upper surface of thephotosensitive layer to protect for reuse an image-bearing negative ortransparency superposed thereon or to improve contact or alignment withthe photosensitive surface. If desired, the photosensitive element canalso have on the reverse surface of the support a pressure-sensitiveadhesive layer provided with a protective strippable layer. Upon removalof the latter the element can be processed onto or otherwise adhered toa permanent support, e.g., a printing block or metal plate.

The photosensitive compositions of this invention can be prepared inmany ways by admixing the three essential constituents specified above.,i.e., (A) the compatible solvent-soluble thermoplastic-elastomeric blockcopolymer compounds described above, (B) the addition-polymerizable,ethylenically unsaturated compound containing at least one terminalvinylidene group, and, uniformly dispersed throughout, (C) anaddition-polymerization initiator activatable by actinic radiation. Forexample, flowable or extrudable compositions can be made by mixing themand other desired adjuvants in any order and, if desired, with the aidof a solvent, e.g., chlorinated hydrocarbons, e.g., chloroform, carbontetrachloride, trichloroethylene and chlorotoluene; ketones, e.g.,methyl ethyl ketone, diethyl ketone and methyl isobutyl ketone; aromatichydrocarbons, e.g., benzene, toluene and xylene; and tetrahydrofuran.The above solvents can contain as diluents small amounts of acetone,lower molecular weight alcohols, e.g., methyl, ethyl, propyl; aliphatichydrocarbons such as petroleum ether and solvent naphtha; and esters,e.g., methyl, ethyl and butyl acetate. The solvent can be removed laterby heating the admixture or extruded layer.

Conventional milling, mixing, and solution techniques can be used inmaking the compositions, the particular technique varying with thedifferences in properties of the respective components. The homogeneous,essentially nonlight scattering compositions are formed into sheets inany desired matter. For example, solvent-casting, hot pressing,calendering, or extrusion are suitable methods for preparing layers ofthe desired thickness.

Actinic radiation from any source and of any type can be used in theseinitiated processes. The radiation may emanate from point sources or bein the form of parallel rays or divergent beams. By using a broadradiation source, relatively close to the image-bearing transparency,the radiation passing through the clear areas of the transparency entersas divergent beams and thus irradiates a continually diverging area inthe photopolymerizable layer underneath the clear portions of thetransparency, resulting in a polymeric relief having its greatest widthat the bottom of the photopolymerized layer, i.e., a frustum, the topsurface of the relief being the dimensions of the clear area. Inasmuchas the free-radical-generating addition-polymerization initiatorsactivatable by actinic radiation generally exhibit their maximumsensitivity in the ultraviolet range, the radiation source shouldfurnish an effective amount of this radiation. Such sources includecarbon arcs, mercury-vapor lamps, fluorescent lamps with specialultraviolet-light-emitting phosphors, argon glow lamps, and photographicflood lamps. Of these, the mercury-vapor lamps, particularly the sunlampor "black light" type, and the fluorescent sunlamps, are most suitable.

When highly reflective supports are used, oblique rays passing throughclear areas in the image-bearing transparency will strike the surface ofthe base at an angle other than 90° and after reflection will causepolymerization in the nonimage areas. This disadvantage can be overcomewhen the photosensitive layer is on a radiation-reflective support by anintervening stratum sufficiently absorptive of actinic radition so thatless than 35% of the incident radiation is reflected. The layerabsorptive of reflected radiation or nonradiation scattering layer, orantihalation layer, can be made by dispersing a finely-divided dye orpigment which substantially absorbs actinic radiation in a solution oraqueous dispersion of a resin or polymer which is adherent to both thesupport and the photoinsolubilized image and coating it on the supportto form an anchor layer which is dried. Suitable antihalation pigmentsinclude carbon black, manganese dioxide, dyes, e.g., Acid Blue Black (CI20470) and Acid Magenta O (CI 42685). A dyed metal plate is also useful.

The antihalation layer intermediate between the photosensitive layer andthe reinforcing support when used must have adequate adhesion to thereinforcing support and the photosensitive layer and not react with theradiation-absorptive material. Suitable polymeric or resin carriers forthe radiation-absorptive dyes or pigments which can be used includepolyvinyl compounds, e.g., polyvinyl chloride homopolymers, andcopolymers, e.g., vinyl chloride with vinyl acetate, diethyl fumarate orethyl acrylate. Copolymers of acrylic and methacrylic acid may also beused.

The solvent liquid used for washing or "developing" the plates made fromthe photosensitive compositions of this invention should have goodsolvent action on the solvent-soluble thermoplastic elastomeric blockcopolymer/ethylenic composition and little action on the insolubilizedimage or upon the support material, antihalation layer, or anchor layerin the period required to remove the nonpolymerized or noncrosslinkedportions. Methyl ethyl ketone, benzene, toluene, xylene, carbontetrachloride, trichloroethane, trichloroethylene, methylchloroform,tetrachloroethylene, etc. are particularly useful solvents. Best resultsare sometimes obtained when the solvent is warm, e.g., 30°-50° C. orwhen the solvent is used in a mixture with a nonsolvent, e.g.,trichloroethylene with ethanol. Incorporation of such nonsolventsreduces swelling of the insolubilized image.

In the development step where the relief is formed, the solvent may beapplied in any convenient manner, as by pouring, immersion, spraying, orroller application. Brushing aids in the removal of the unpolymerized oruncrosslinked portion of the composition.

The printing reliefs made in accordance with this invention can be usedin all classes of printing but are most applicable to those classes ofprinting wherein a distinct difference of height between printing andnonprinting areas is required and particularly to the flexographicprinting class wherein a resilient print area is required, e.g., forprinting on deformable printing surfaces. These classes include thosewherein the ink is carried by the raised portion of the relief such asin dry-offset printing, ordinary letterpress printing, the latterrequiring greater height differences between printing and nonprintingareas, and those wherein the ink is carried by the recessed portions ofthe relief such as in Intaglio Printing, e.g., line and invertedhalftone. The plates are also useful for multicolor printing.

The photosensitive elements of this invention are also useful in thepreparation of photoresists for etching, plating, etc.; planographic andgravure plates, and screens for "silk screen" printing or as stencils.The elements, upon removal of the support can be attached to printingcylinders, e.g., plastic or metal cylinders.

The photosensitive elements are suitable for other purposes, in additionto the printing uses described above, in which readily insolubilized,solid, addition polymerizable elements are useful, e.g., as ornamentalplaques or for producing ornamental effects; as patterns for automaticengraving machines, foundry molds, cutting and stamping dyes; for namestamps; for relief maps; in the preparation of printed circuits; and inthe preparation of other plastic or elastomeric articles.

The invention will be further illustrated by but is not intended to belimited to the following examples wherein parts and percentages are byweight.

EXAMPLE I

A photosensitive, thermoplastic, elastomeric solid sheet was prepared bythe following procedure: a solution of 0.0467 g 2-ethylanthraquinone and0.0924 g p-methoxyphenol in a small amount of tetrahydrofuran was addedto 4.33 g trimethylolpropane triacrylate. This mixture was added to acyclohexane solution (140 ml) of 30.16 gpolystyrene-polybutadiene-polystyrene block copolymer (MW˜76,000) and0.06 g 2,6-di-tert-butyl-4-methylphenol and was then heated to 60° C.and stirred vigorously for two hours. (The polybutadiene block having aglass transition temperature about minus 85° C. comprises 69% by weightof the block copolymer which has a solution viscosity of 4000 cps(measured as a 25% by weight toluene solution with a BrookfieldViscometer Model LVF using a spindle number 3 at 6 rpm with scale factorof 200), a specific gravity of 0.95 and 800% elongation (obtained forfilms cast from 25% by weight toluene solution), the polystyrene blockshave glass transition temperatures of approximately 100° C.). Theresulting homogeneous solution was degassed in an oven at 70° C. forseveral hours until a porous rubber foam remained. This solid wasfurther degassed under vacuum at 60° C. overnight and then molded into a0.030 inch thick clear layer between two sheets of 0.002 inch, uncoated,biaxially oriented, heat set, polyethylene terephthalate film in aplaten press at 110° C. using 0.033 inch spacers by applying 16 psipressure for several minutes. After stripping off the polyester coversheet half the layer was exposed for 40 minutes to actinic radiationfrom a bank of four parallel 15 W General Electric Blacklight lamps(F15T8-BLB) (lamp center 1.5 inches apart) at a distance of 3 inches.When subsequently immersed in tetrahydrofuran overnight, the exposedhalf of the layer swelled slightly in contrast to the unexposed halfwhich dissolved in tetrahydrofuran within a few minutes.

EXAMPLE II

A 0.064 inch thick photosensitive elastomeric sheet was prepared as inExample I with the use of suitable spacers on the platen press. Afterremoving the polyester cover sheet the photosensitive sheet wasconditioned under nitrogen gas for two days and was then imagewiseexposed for 20 minutes through an image-bearing transparency to actinicradiation as described in Example I. The sheet was then washed intetrahydrofuran for 2.25 minutes producing a deep relief image which wassubsequently dried, conditioned with nitrogen gas and post-exposed toactinic radiation as described in Example I for 2.5 hours. The reliefassembled a molded vulcanized rubber relief.

EXAMPLE III

A solution of 30.01 g of polystyrene-polybutadiene-polystyrene blockcopolymer of Example I, 4.02 g 1,4-butane-diol diacrylate, 0.0448 g2-ethylanthraquinone, 0.06 g 2,6-di-tert-butyl-4-methylphenol and 0.087g p-methoxyphenol in 40 ml cyclohexane was prepared as in Example I andthen solvent was removed by heating the solution to 70° under vacuum.After drying the same at 60° C. under vacuum overnight it was moldedbetween two sheets of 0.002 inch, biaxially oriented, heat set,polyethylene terephthalate film at 110° C. and 16 psi for 15 minutes ina platen press using suitable spacers to give a 0.064 inch thick sheet.After removing the polyester cover sheet the sample was conditioned tonitrogen gas 4 hours, imagewise exposed for 16 minutes through animage-bearing transparency to actinic radiation as in Example II andsubsequently washed in tetrahydrofuran for 1 minute. The resultingelastomeric deep relief plate was further conditioned in nitrogen gasfor two days and then post-exposed to actinic radiation as in ExampleII. When the surface of this elastomeric relief inked with an alcoholbased ink was pressed to a paper sheet a printed image resulted whichfaithfully reproduced a negative of the original image transparency.

EXAMPLE IV

A photosensitive, thermoplastic, elastomeric solid sheet was preparedfrom 156.3 g polystyrene-polyisoprene-polystyrene block copolymer(MW˜100,000), 23.4 g trimethylolpropane trimethacrylate, 0.216 g2-ethylanthraquinone, 0.12 g p-methoxyphenol, and 0.313 g2,6-di-tert-butyl-4-methylphenol using procedures as in Example III.(The polyisoprene block has a glass transition temperature about minus72° C. and comprises 85% by weight of the block copolymer which has asolution viscosity of 1600 (measured as in Example I); a specificgravity of 0.93; a hardness of 37 as determined with a Shore® Type Adurometer (a product of the Shore Instrument & Mfg. Co., Inc.), andhereinafter expressed as "Shore® A hardness of"; and 1300% elongation(for film cast from 25% by weight toluene solution).) One of thepolyester cover films was stripped off and the sample conditioned forone day in nitrogen gas. It was imagewise exposed for 25 minutes throughan image-bearing transparency placed in contact with the photosensitivesurface using the radiation source described in Example I. The exposedsurface was spray washed with methyl chloroform for 4.5 minutes. Thesheet with the relief was then post-exposed through the polyester basefor 50 minutes to the same radiation source producing a highly resilientrelief firmly adhered to the polyester support.

EXAMPLE V

A photosensitive, thermoplastic, elastomeric sheet was prepared bydissolving 3.5 g benzoin methyl ether in 35 g hexamethylene glycoldiacrylate. The solution was added to 659.9 gpolystyrene-polyisoprene-polystyrene block copolymer (described inExample IV) and 1.6 g 2,6-di-tert-butyl-4-methylphenol in a 1 gallonbottle and the components were mixed by manual shaking. Five batches ofthe mixture were fed continuously into a 20×1 inch single screw extruder(Killion, model #K100). The mix was extruded at 170° C. and 42 rpm forabout 5 minutes (˜3.0 kg per hour) and came out through a 4×0.030 inchsheeting die and was quenched on a water chilled casting wheel to form4×0.040 inch sheet. About 80 g of this sheet was hot pressed between two8×8 inch sheets of 0.002 inch, uncoated, biaxially oriented and heat setpolyethylene terephthalate film into a 0.110 inch plate with a PasadenaHydraulic Inc. press at 100° C. and 20,000 lb. pressure using two 0.110inch spacers. The top polyester sheet was subsequently removed and theplate was laminated with a 0.00075 inch polyethylene film using a rubbersequeegee. The plate's polyethylene side was covered with animage-bearing transparency and placed in a vacuum frame. The plate wasthen imagewise exposed for 5 minutes under vacuum with a bank of fourparallel 40 watt ultraviolet fluorescent lamps (Sylvania,FR48T12-BL-VHO-180 Blacklite) in conventional lamp holder at a 4 inchdistance. Lamp centers were 2 inches apart and two cooling fans wereused to reduce heat build up. After exposure, the polyethylene sheet wasremoved and the surface of the eleastomeric plate was washed with aplush brush wet with 3:1 methylchloroform and ethanol solvent mixtureproducing a relief image on the plate. The plate was dipped in a 2%solution of 2,6-di-tert-butyl-4-methylphenol in 3:1 methylchloroform andethanol solvent mixture. The wet plate was post-exposed in air for 10minutes using the same radiation source described above. The plate had aShore® A hardness of 45. The polyester backing sheet was stripped offand the plate was mounted on a 15 inch circumference solid cylinder withdouble sided adhesive tape. The cylinder was mounted in a Kidder GIpress (36 inch wide) fitted with a 200 line per inch Anilox roll."Polyprint Beckerman Red" #40-0-3478 ink, a product of Del Val, Inc. wasused. Stock was 0.00125 inch extruded polyethylene and was supplied inrolls of 13 inch diameter and each roll yielded approximately 3000impressions. The flexographic plate made a press run of 195,000impressions and showed no sign of wear. The print quality from thisplate is at least equivalent to that from a plate made conentionallyfrom natural rubber.

EXAMPLE VI

A photosensitive, thermoplastic, elastomeric solid sheet was preparedfrom 1.1 g poly-α-methylstyrene-polybutadiene-poly-α-methylstyrene blockcopolymer (MW˜115,000, 25% poly- -methylstyrene having a glasstransition temperature of 175° C.), 0.23 g hexamethylene glycoldiacrylate, 0.16 g naphthenic oil, 0.015 g2,6-di-tert-butyl-4-methylphenol, 0.0011 g benzoin methyl ether usingprocedures as in Example III. One of the polyester cover sheets wasremoved and the photosensitive sheet was laminated with a 0.00075 inchpolyethylene film. The sample was exposed through an image-bearingtransparency (placed on the polyethylene cover sheet) in a vacuum framefor 25 minutes to actinic radiation (described in Example I). Thepolyethylene film was stripped off and the exposed elastomeric sheet wasdeveloped by brushing in methylchloroform for 4 minutes. The sample wasthen post-exposed to the same radiation source for 30 minutes. Theresulting elastomeric sheet had a 0.027 inch relief image and resembledmold vulcanized rubber relief. When cemented to a wood block the reliefcould be used with an ink pad as a rubber stamp.

EXAMPLE VII

A photosensitive, thermoplastic, elastomeric sheet was prepared,imagewise exposed and processed as in Example VI except that 1.1 gpoly-α-methylstyrene-polyisoprene-poly-α-methylstyrene (MW˜82,000, 30%poly-α-methylstyrene) was used instead ofpoly-α-methylstyrene-polybutadiene-poly-α-methylstyrene. The elastomericrelief produced was 0.030 inch and could be used as a rubber stamp toprint on paper or other stock.

EXAMPLE VIII

Fourteen thermoplastic elastomeric sheets were prepared frompolystyrene-polyisoprene-polystyrene block copolymer (described inExample IV and designated SIS); the antioxidant,2,6-di-tert-butyl-4-methylphenol, designated AO; either one of the twopolymerization initiators activatable by actinic radiation, 2-ethylanthraquinone, designated PI-1, and benzoin methyl ether, designatedPI-2; and one of the ethylenically unsaturated compounds listed in thefollowing table and in the amount designated:

    ______________________________________                                                Grams    Ethylenically                                                Sheet   Used     Unsaturated Compound                                         ______________________________________                                        1       36.7     hexamethylene glycol dimethacrylate                          2       36.7     2,2,4-trimethyl-1,3-pentanediol                                               dimethacrylate                                               3       11.8     decamethylene glycol diacrylate                              4       36.7     diallyl fumarate                                             5       36.7     1,3,5-triisopropenyl benzene                                 6        3.5     2,2-di(p-hydroxyphenyl)-propane                                               dimethacrylate                                               7        5.6     polyoxyethyl-2,2-di(p-                                                        hydroxyphenyl) propane                                                        dimethacrylate                                               8        5.0     t-butyl acrylate                                             9        5.0     N,N--diethylaminoethyl acrylate                              10       3.8     butylene glycol dimethacrylate                               11      15.0     1-phenylethylene-1,2-dimethacrylate                          12      15.0     styrene                                                      13      15.0     1,4-diisopropenyl benzene                                    14      10.0     2,2-di(p-hydroxyphenyl)-propane                                               diacrylate                                                   ______________________________________                                    

The grams of the other components used in each sheet are tabulated inthe following table:

    ______________________________________                                        Sheet      SIS     AO         PI-1 PI-2                                       ______________________________________                                        1          199.5   0.5        0.6  0                                          2          199.5   0.5        0.6  0                                          3          223.4   0.6        0.59 0                                          4          199.5   0.5        0.6  0                                          5          199.5   0.5        0.6  0                                          6          29.92   0.08       0.06 0                                          7          49.27   0.13       0.14 0                                          8          44.89   0.11       0.09 0                                          9          44.89   0.11       0.09 0                                          10         59.75   0.25       0.12 0                                          11         84.79   0.21       0    0.5                                        12         84.79   0.21       0    0.5                                        13         84.79   0.21       0    0.5                                        14         188.15  0.5        0    0.8                                        ______________________________________                                    

Sheets 6 through 10 were prepared as in Example IV and the other sheetswere prepared as in Example XVII. As in Example IV each of the sheetswas imagewise exposed for about 45 minutes to actinic radiation and thenspray-washed for 4 minutes with a 7:3 solvent mixture of methyl ethylketone and methylchloroform. Each resulting elastomeric printing reliefresembled conventional natural rubber flexographic printing plates intheir durability and the quality of the printed stock.

EXAMPLE IX

Seven thermoplastic elastomeric sheets were prepared frompolystyrene-polyisoprene-polystyrene block copolymer (described inExample IV and designated SIS); the antioxidant,2,6-di-tert-butyl-4-methylphenol, designated AO; either one of the twoethylenically unsaturated compounds, hexamethyleneglycol diacrylate,designated HD, and trimethylolpropane trimethacrylate, designated TT;and one of the polymerization initiators listed in the following table.Also included in the table are the number of grams of each componentused in the sheets.

    ______________________________________                                        Sheet   Initiator    SIS     AO    HD   TT                                    ______________________________________                                        1       0.70 g benzo-                                                                              50.01   0.13  9.5  0                                             phenone                                                                       0.01 g 4,4'-bis-                                                              (dimethyl-amino)-                                                             benzophenone                                                          2       0.5 g benzoin                                                                              93.17   0.23  5.0  0                                             methyl ether                                                                  0.5 g trimethyl-                                                              phosphine                                                             3       0.5 g α-tert-                                                                        94.26   0.24  5.0  0                                             butyl benzoin                                                         4       0.92 g 2-tert-                                                                             299.25  0.75  0    55.02                                         butyl anthra-                                                                 quinone                                                               5       1.20 g benzoin                                                                             105.14  0.26  6.0  0                                     6       0.5 g benzoin                                                                              94.26   0.24  5.0  0                                             acetate                                                               7       0.8 g benzil 112.92  0.28  6.0  0                                     ______________________________________                                    

The first sheet was prepared as in Example IV and the others as inExample XVIII. As in Example IV each of the seven sheets was imagewiseexposed to actinic radiation, processed to produce a relief image. Eachresulting elastomeric printing relief produced image quality comparableto that of conventionally molded natural rubber plates and for sheet "3"the print quality was superior to the others and required less exposureto insolubilize the exposed areas.

EXAMPLE X

A polystyrene-polybutadiene-polystyrene block copolymer (MW˜100,000,wherein the polybutadiene block, of which about 40% by weight is formedby 1,2 addition-polymerization and about 60% by 1,4addition-polymerization, comprises 75% by weight of the block copolymer)was hydrogenated as taught in Jones U.S. Pat. No. 3,431,323. Thepolybutadiene block was more than 95% hydrogenated whereas thepolystyrene blocks were less than 10% hydrogenated. 80 g of thehydrogenated block copolymer, 8.0 g hexamethylene glycol diacrylate, 0.2g 2-ethylanthraquinone, 0.8 g 2,6-di-tert-butyl-4-methylphenol, and 0.4g p-methoxyphenol were roll-milled for 20 minutes at 155° C. and thenpressed, into a plate at 140°-150° C. as in Example V, into a 0.110 inchthick sheet except that one of the cover sheets used was a 0.04 inchresin coated polyethylene terephthalate film described in Example IV ofAlles, U.S. Pat. No. 2,779,684. The plate was imagewise exposed for 20minutes as in Example V. The uncoated polyethylene terephthalate coverfilm was then stripped off and the plate was developed by spray washingwith toluene for 1.5 minutes producing a relief image. The developedplate was dried and then post-exposed to actinic radiation described inExample V through the resin coated support for 30 minutes producing asupported elastomeric relief image useful for flexographic printing andwith greater resistance to oxidative attack than conventionally preparednatural rubber printing plates.

EXAMPLE XI

A photosensitive, thermoplastic, elastomeric sheet was prepared as inExample X except that the block copolymer was essentially completelyhydrogenated removing both the butadiene as well as the styreneunsaturation. A second photosensitive thermoplastic elastomeric sheetwas similarly prepared with 110 g of the above hydrogenated blockcopolymer, 8 g trimethylolpropane trimethacrylate, 0.2 g2-ethylanthraquinone, 1.1 g 2,6-di-tert-butyl-4-methylphenol, and 0.40 gp-methoxyphenol. An elastomeric relief plate firmly adhered to thecoated polyethylene terephthalate support was produced from each of thetwo photosensitive sheets when imagewise exposed and processed as inExample X. Compared to conventionally prepared natural rubber plates,the above elastomeric printing plates could be used longer forflexographic printing before ozone and oxidative attack of the platesinterfered with print quality.

EXAMPLE XII

80 g Of the partially hydrogenated block copolymer described in ExampleX, 12 g trimethylolpropane triacrylate, 0.8 g benzoin methyl ether, and0.8 g 2,6-di-tert-butyl-4-methylphenol were roll-milled at 155° C. untilhomogeneously mixed. The mixture was then hot pressed into a 0.110 inchsheet between two 0.002 inch, uncoated, biaxially oriented, heat setpolyethylene terephthalate film as in Example V. A secondphotosensitive, thermoplastic, elastomeric sheet was prepared as aboveexcept that 80 g of the fully hydrogenated block copolymer described inExample XI was substituted for the above partially hydrogenated blockcopolymer. After one of the polyester cover sheets was replaced with apolyethylene film each sample was imagewise exposed for 30 minutes as inExample V. The polyethylene film was stripped off and each sample wasspray washed with toluene for 2 minutes producing an elastomeric reliefwhich upon drying and subsequent post-exposure to the same radiation asabove for 10 minutes was used as a printing plate for printing onpolyethylene stock. The resistance of both printing plates to ozoneattack was substantially better than similar printing plates producedconventionally from natural rubber.

EXAMPLE XIII

Photosensitive, thermoplastic, elastomeric sheet was prepared by thefollowing procedure: 2166 g polystyrene-polyisoprene-polystyrene blockcopolymer (described in Example IV), 180 g hexamethylene glycoldiacrylate, 22.5 g benzoin methyl ether, 5.4 g2,6-di-tert-butyl-4-methylphenol, 240 g napthenic oil, 360 gα-methylstyrene-vinyltoluene copolymer (melt viscosity at 160° C. isabout 10 poises), and 30 g microcrystalline wax were mixed as in ExampleV and the mixture fed through a melt extruder. The material was extrudedat about 115° C. through a 6 inch wide die. The extrudate was quenchedin cold water for about 10 minutes. It was subsequently pre-heated to85° C. and then calendered at about 110° C. between two polyester sheetsin an Adamson United four roll laboratory calender to give anelastomeric photosensitive layer 0.11 inch thick. One of the polyestersheets was 0.002 inch, uncoated, biaxially oriented, heat setpolyethylene terephthalate; the other sheet was 0.004 inch, biaxiallyoriented, heat relaxed, polyethylene terephthalate coated with a thinresin coating as in Example X. The 0.002 inch polyester cover sheet wasreplaced with a 0.005 inch thick polypropylene film and the sample wasexposed for 20 minutes as in Example V through a transparency bearingthe negative image of a gasket. With the polypropylene cover filmremoved, the sample's elastomeric surface was washed with a brush wetwith a 3:1 mixture of trichloroethylene and alcohol. The sample was thendried, post-exposed to the same actinic radiation as above for 10minutes and the remaining polyester support stripped away. The resultingelastomeric gasket was 0.105 inch thick with a Shore®A hardness of 45.It closely resembled a positive of the original transparency and couldbe compressed or stretched without permanent deformation. A secondcomplicated gasket was similarly produced from a transparency bearingthe negative image of an irregular honeycomb.

EXAMPLE XIV

A photosensitive element useful in preparing deep relief letterpressprinting plates was prepared as follows:

A primed support, using tin-plated steel 16 inches wide and 0.0063 inchthick was prepared as described in Example III of German Pat. No.1,959,716 issued May 3, 1967.

An adhesive composition was composed of (A) 100 grams of a solution of18% solids in a mixed solvent consisting of dioxane, toluene andcyclohexanone (30/46/2), the solids consisting of a copolyester preparedfrom a reaction mixture of an excess of ethylene glycol and dimethylterephthalate, dimethyl isophthalate, dimethyl sebacate and dimethyladipate in a molar ratio of the latter four reactants of 4:4:1:1respectively, (B) 3.33 grams of the polyisocyanate solution described inExample I of German Patent 1,959,716, and (C) 11.25 grams of a solutionof 20% solids in a mixed solvent consisting of methyl ethyl ketone anddioxane (1/1), the solids consisting of the epoxy resin described inExample I of German Pat. No. 1,959,716.

This adhesive composition was coated on the primed, tin-plated steelsupport forming an adhesive composition layer about 0.0015 inch thick.The adhesive composition was dried and cured by heating for 1 minute at230° C. resulting in an adhesive layer about 0.0003 inch thick.

A barrier solution was composed of (A) 100 grams of a solution of 20%solids in a mixed solvent consisting of methyl ethyl ketone and methylCellosolve®(7/3), the solids consisting of a photopolymerizablecomposition prepared in a manner similar to that disclosed in Example Iof Smith U.S. Pat. No. 3,012,952 and (B) 1.60 grams of benzoyl peroxide(thermal initiator).

The barrier composition was coated on the adhesive coated supportforming a barrier composition layer about 0.005 inch thick. The barriercomposition was dried and cured by heating for 1 minute at 230° C.,resulting in a partly polymerized barrier layer about 0.001 inch thick.

A photosensitive thermoplastic elastomeric layer was prepared as inExample III from the following components: 61.69 gpolystyrene-polybutadiene-polystyrene block copolymer (Example I), 16.0g 1,4-butanediol diacrylate, 0.20 g 2-ethylanthraquinone, 0.25 gp-methoxyphenol and 0.15 g 2,6-di-tert-butyl-4-methylphenol. This layerwas laminated to the coated, tin-plated steel support described above byheat pressing at 230° C. between the support and an uncoated polyestercover sheet for 25 minutes using 0.03 inch spacers. After the polyestercover sheet was removed the photosensitive sheet was imagewise exposedas in Example II for 25 minutes and then was spray washed withtetrahydrofuran for 4-5 minutes. The resulting relief was 0.028 inchdeep and, after post-exposure, as in Example II had a Shore®D hardnessof 43. The relief image was resilient, elastic and free from brittlenessand the letterpress printing plate could be bent through an angle of180° without the relief cracking. The plate was placed on a printingcylinder 4 inches in diameter, inked and used for printing. Satisfactoryprinted reproductions of the negative of the image transparency wereobtained.

EXAMPLE XV

A photosensitive, thermoplastic elastomeric sample was prepared from thefollowing components using the procedures in Example III: 50 gpolystyrene-polyisoprene-polystyrene block copolymer (described inExample IV), 2.8 g polyoxypropyl trimethylolpropane triacrylate (MW462), and 0.21 g benzoin methyl ether. The sample was pressed into a0.040 inch sheet as in Example III except that one polyester cover sheetwas replaced with an uncoated 0.002 inch polyimide film prepared as inExample 19 of U.S. Pat. No. 3,179,634. The polyester cover sheet wasremoved and the sample was imagewise exposed as in Example IV for 15minutes in a reduced pressure of nitrogen gas. The sheet was thenspray-washed 3.5 minutes with a 7:3 solvent mixture of ethylacetate andmethylchloroform. The elastomeric relief when used as in Example IIIfaithfully reproduced a negative of the original image transparency.

EXAMPLE XVI

Five samples each weighing 120 g were prepared, exposed and processed asin Example XVII, except that each contained 5% by weighthexamethyleneglycol diacrylate, 0.5% by weight benzoin methyl ether,0.2% by weight 2,6-di-tert-butyl-4-methylphenol and one of the followingcomponents:

    ______________________________________                                                % by                                                                  Sheet   Weight     Component                                                  ______________________________________                                        1       0.3        1,3,5-trimethyl-2,4,6-tri(3,5-di-                                             tert-butyl-4-hydroxybenzyl)benzene                         2       0.3        2-(4-hydroxy-3,5-tert-butylaniline)-                                          4,6-bis(n-octylthio-1,3,5-                                                    triazine)                                                  3       1.5        1,1,3,3-tetramethyl-2-thiourea                             4       10.0       linseed oil                                                5       15.0       α-methylstyrene vinyl toluene                                           copolymer (melt viscosity 140° C.                                      35 poise)                                                  ______________________________________                                    

When compared to the photosensitive sheet in Example XVII, Sheets 1 and2 were less sensitive to the presence of oxygen. Similarly printingreliefs prepared from Sheets 3, 4 and 5 were less susceptible to defectscaused by ozone attack, cracking with age and flexing.

EXAMPLE XVII

A photosensitive, thermoplastic elastomeric layer was prepared from180.3 g polystyrene-polyisoprene-polystyrene block copolymer (describedin Example IV), 10.0 g hexamethylene glycol diacrylate, 1.0 g benzoinmethyl ether, 0.45 g 2,6-di-tert-butyl-4-methylphenol, 0.6 g2,2-methylene-bis-(4-methyl-6-tert-butylphenol), 0.6 gdilaurylthiodipropionate, 5.0 g 3-cyclohexenylidene methylbenzyl ether,and 2 g microcrystalline wax. The ingredients were roll milled at 120°C. in a Thropp 6×12 rubber mill and then the mixture was pressed intosheet and subsequently imagewise exposed for 10 minutes as in Example V.The exposed surface was spray washed 4 minutes with a 7:3ethylacetate:methylchloroform solvent mixture, was dried and thenpost-exposed 10 minutes. The elastomeric relief after six months storagehad no indications of cracking due to ozone attack. Similarly a reliefmade the same way and elongated by 25% by looping had no apparent ozonedamage after 6 days. Both reliefs when mounted on a press and inkedproduced satisfactory printed images.

EXAMPLE XVIII

A photosensitive, thermoplastic elastomeric layer between polyestercover sheets was prepared as in Example XVII using the followingcomponents: 232.42 g polystyrene-polyisoprene-polystyrene blockcopolymer (described in Example IV), 2.36 g hexamethylene glycoldiacrylate, 0.59 g 2-ethylanthraquinone and 0.58 g2,6-di-tert-butyl-4-methylphenol. After imagewise exposure as in ExampleIII for 25 minutes the exposed surface was spray washed with a 3:2solvent mixture of 2-butanone and methylchloroform. The sample was driedand post-exposed for 45 minutes to actinic radiation described inExample I producing an elastomeric relief 0.024 inch deep and with aShore®A hardness of 43. An elastomeric relief 0.250 inches thick wassimilarly prepared and when used as a flexographic printing plate usingcorrugated paper stock produced print quality at least comparable tothat produced from a conventional rubber plate.

EXAMPLE XIX

A photosensitive layer was prepared using the following components:30.04 g polystyrene-polybutadiene-polystyrene block copolymer (describedin Example I), 100 ml cyclohexane, 7.46 g triethyleneglycol diacrylate,0.0711 g 2-ethylanthraquinone, 0.0872 g p-methoxyphenol, and 0.06 g2,6-di-tert-butyl-4-methylphenol. The block copolymer and2,6-di-tert-butyl-4-methylphenol were refluxed in cyclohexane until aviscous solution formed after which the other components were added incyclohexane solution. The mixture was heated and stirred until a clearsolution was formed. The solution was then heated in vacuum at 70° C. toremove the solvent. The resulting material was pressed between twosheets of aluminum foil into a 0.030 inch elastomeric sheet as inExample I and similarly exposed. A transparent film resulted which washarder than the unexposed film and did not dissolve when immersed intetrahydrofuran for 16 hours.

EXAMPLE XX

A solution of 22.79 g polystyrene-polyisoprene-polystyrene blockcopolymer (described in Example IV), 20.00 g 2,2-dimethylolpropanediacrylate, 0.50 g benzophenone, 0.15 g4,4'-bis(dimethylamino)benzophenone, 0.06 g2,6-di-tert-butyl-4-methylphenol, 1.5 g naphthenic oil and 5 gpentaerythritol ester of hydrogenated rosin in 100 ml methylchloroformwas prepared and coated on a 0.004 inch film of polytetrafluoroethyleneusing a 0.006 inch doctor knife. After drying, the photosensitive layerwas laminated to the copper surface of a copper clad epoxy fiber glassboard by heat pressing at 105° C. The polytetrafluoroethylene coversheet was stripped off and replaced with a 0.001 inch polypropylene filmand imagewise exposed for 5 minutes as in Example V. The cover sheet wasdiscarded and the exposed surface was brushed for 3.5 minutes with a 3:7methylchloroform:ethylacetate solvent mixture and the plate was immersedin agitated ferric chloride solution at 40° C. Areas corresponding tothe unexposed portions of the layer were etched away and the remainingexposed layer was removed with trichloroethylene forming a negativecopper image of the original transparency.

EXAMPLE XXI

A photosensitive layer laminated to a copper-clad epoxy fiber glassboard with a polypropylene cover sheet was prepared as in Example XX.The photosensitive layer was exposed through a transparency bearing theimage of a printed circuit for 5 minutes using a nuArc Plate Maker ofthe flip-top type using a Xenon Arc source, Model No. FT-261manufactured by the nuArc Co., Inc., Chicago, Ill. The unexposedportions of the layer were then removed as in Example XX forming anegative resist image of the printed circuit. The resist board wasrinsed with water then dipped in 25% sulfuric acid for 20 seconds,followed by a water rinse, and then a rinse in 25% ammonium persulfatesolution for 25 seconds. The board was rinsed once again in water andthen dipped in 25% sulfuric acid for 20 seconds and finally rinsed withdistilled water.

The resist copper board was placed in a copper pyrophosphate platingbath of the following composition:

Copper (Cu⁺²)--30 g/l

Pyrophosphate (P₂ O₇ ⁻⁴)--200 g/l

Nitrate(NO₃ ⁻¹)--8 g/l

Ammonia (NH₃)--2 g/l

Orthophosphate (HPO₄ ⁻²)--0.1 g/l

This bath was held at pH 8.2, and 122° F. The weight ratio ofpyrophosphate to copper was 7.5. The bath was operated at 1.5 volts witha cathode current density of 30 ampheres/sq. ft. Copper was deposited inan electroplating bath for 15 minutes on the unprotected nonresist areasof the imaged copper-clad board after which it was removed from the bathand dried in air.

The electrolytically-deposited copper of the resist board was thenplated over with gold and then the resist was stripped off usingmethylene chloride. The board was etched in 45° Baume ferric chlorideand formed a pattern plated printed circuit board.

EXAMPLE XXII

A solution of 12.55 g polystyrene-polyisoprene-polystyrene blockcopolymer (described in Example IV), 9.0 g hexamethylene glycoldiacrylate, 0.30 g bis-(2-o-chlorophenyl-4,5-diphenylimidazolyl), 0.15 gtris-(2-methyl-4-diethylaminophenyl)methane, 0.50 g naphthenic oil and2.50 g pentaerythritol ester of hydrogenated rosin in 75 mltrichloroethylene was prepared and coated on a plate of nontreated,brush grained aluminum using a 0.002 inch doctor knife. After drying,the photosensitive surface was laminated with 0.001 inch polypropylenefilm using a squeegee and then imagewise exposed for 2 minutes as inExample V. The polypropylene film was stripped off and the exposed layerwas brush-developed for 2.5 minutes as in Example XX. The aluminum platewith the developed image was gummed with gum arabic and the imagedsurface was wetted with water and applied with standard oleophilicplanographic ink. Areas corresponding to the unexposed regions of theplate did not retain ink whereas areas corresponding to the exposedregions of the plate did. The inked image when pressed to paper stockproduced a negative printed image of the original transparency.

EXAMPLE XXIII

A 0.250 inch photosensitive thermoplastic elastomeric layer wasprepared, exposed, and processed as in Example XVIII, except that priorto exposure both polyester cover sheets were removed. Thephotosensitive, self supporting elastomeric layer could be stretched andmanipulated around a cylinder or other such objects. Upon imagewiseexposure and solvent-washing, a 0.250 inch thick elastomeric layer witha 0.024 inch deep relief was obtained which, as in Example XVIII,produced print quality at least comparable to that produced from aconventional rubber plate.

EXAMPLE XXIV

A polyamide-coated polyester cover film was prepared by coating asolution of 5 g of an alcohol-soluble polyamide resin in 100 ml of 1:1solvent mixture of methanol and chloroform on a 0.002 inch uncoatedbiaxially oriented, heat set, polyethylene terephthalate film using a0.006 inch doctor knife. (The polyamide resin, Elvamide®8061, a productof E. I. du Pont de Nemours and Company, is colorless, transparent, hasa melting point of 300°-320° F., a specific gravity of 1.08 at 73° F.and in a 10% methanol solution at 77° F. has a Brookfield viscosity of30 cp). The coating dried to a 0.00015 inch thick smooth, hard, flexiblefilm.

A 0.110 inch thick photosensitive, thermoplastic elastomeric sheetbetween polyester cover sheets was prepared as in Example XV except thatone of the polyester cover sheets was coated with a polyamide film asdescribed above which was laminated to the photosensitive surface. Theresulting sample could be manipulated with no detrimental effect to thephotosensitive layer. The polyester cover sheet was stripped from thepolyamide surface which adhered to the photosensitive layer. The hard,flexible smooth polyamide surface was covered with an image-bearingtransparency. The position of the transparency in close contact with thepolyamide surface could be easily adjusted. The photosensitive layerimagewise exposed through the polyamide film and transparency for 5minutes as in Example V. The plate was brushed for 3 minutes with a 3:1solvent mixture of trichloroethylene and methanol to produce a reliefimage and remove the polyamide film. When dry, the relief image waspost-exposed as in Example V and when used as a printing relief producedprint images which faithfully reproduced a negative of the imagetransparency.

EXAMPLE XXV

A photosensitive, thermoplastic, elastomeric layer containing 70.25parts by weight of polystyrene-polyisoprene-polystyrene block copolymer,5.0 parts hexamethylene glycol diacrylate, 0.75 part benzoin methylether, 15.0 parts α-methyl styrene vinyl toluene resin, 8.0 partsnaphthenic mineral oil, 1.0 part synthetic ceresin wax, and about 0.12part 2,6-di-tert-butyl-4-methylphenol and laminated on each side with apolyester sheet was prepared as in Example XIII except that the 0.002inch heat set polyethylene terephthalate cover sheet was first coatedwith a solvent-soluble, hard, flexible film. The coated surface of thecover sheet was then laminated to the photosensitive layer during thecalendering process as in Example XIII.

The coated cover sheet was prepared by coating a solution of 300 gpolyethylene-polyvinyl acetate copolymer (Elvax®420, a product of E. I.du Pont de Nemours and Company; 18% vinyl acetate; melt index of 125-175g/10 minute using the procedure ASTM D-1238), 27 g stearic acid in 2liters trichloroethylene on 0.002 inch, uncoated, biaxially oriented,heat set, polyethylene terephthalate film using a 0.006 inch doctorknife and then drying at 180° F.

The photosensitive sample could be manipulated and could be stored forseveral months with no significant change in sensitivity. The 0.002 inchpolyester cover sheet was stripped from the polyethylene-polyvinylacetate copolymer coating which adhered to the surface of thephotosensitive layer. The photosensitive sheet was then exposed for 5minutes to actinic radiation through an image-bearing transparency onthe copolymer-coated surface using a Dycril® photopolymer printing platerotary exposure unit, Model 3832 RCL, a product of E. I. du Pont deNemours and Company. The hard, flexible copolymer-coated surface did notseparate from the photosensitive layer when the sheet was flexed andmanipulated and insured uniform close contact of the transparency to thesheet during exposure to actinic radiation.

The exposed sample was brushed for five minutes with 3:1 solvent mixtureof trichloroethylene and ethanol to remove the copolymer coating andunexposed areas of the photosensitive elastomeric layer. The resultingsupported relief plate was dried and post exposed as in Example V andwhen used as a flexographic printing plate gave print quality at leastequivalent to that from conventionally made rubber plates.

EXAMPLE XXVI

A photosensitive element was prepared as in Example XXV and was thenexposed through the 0.004 inch, heat relaxed polyethylene terephthalatesupport sheet to actinic radiation from a parallel bank of threeWestinghouse FS 20 fluorescent sunlamps at a distance of 1.5 inches for10 minutes. Then, as in Example XXV, the 0.002 inch, heat setpolyethylene terephthalate cover sheet is stripped from the element,which was imagewise exposed for 4 minutes, and developed to produce arelief image suitable for flexographic printing.

The relief produced from the pre-exposed element was improved over thesimilar relief produced in Example XXV in that the depth of thedeveloped relief was limited to 0.035 inch, the background areas did notshow brush marks and solvent swelling during processing was reducedresulting in shortened drying time. Further advantages were that thedimensional stability of the photosensitive elements prior to imagewiseexposure was improved, thus simplifying storage and handling. Also forsimilar reasons the need to post-expose after imagewise exposure isobviated.

All the elements illustrated in the examples of this invention cancontain a flexible, polymeric film interposed between the cover sheetand the surface of the photosensitive layer. Thus, in accordance withthe invention, one may prepare solvent-insoluble printing reliefs, andflexographic printing plates in particular, by applying a layer of thephotosensitive, elastomeric composition of the invention to a sheetsupport (e.g., polyethylene terephthalate); laminating a flexible,polymeric film (e.g., polyamide or polyethylene-polyvinyl acetatecopolymer) and a flexible cover sheet to said layer, so that the surfaceof the film is contiguous to the surface of the photosensitive layer;stripping the cover sheet from the film; imagewise exposing thephotosensitive layer through the film; and removing said film and theunexposed areas of said layer by solvent washing. The photosensitivecomposition may be applied to the sheet support by coating techniques orby laminating or squeeging at a suitable temperature the compositionbetween the sheet support and the film coated flexible cover sheet. Manyvariations of this preferred process will be apparent to those skilledin the art. For example, the cover sheet and the step of stripping itmay be omitted where storage and handling prior to exposure are notrequired; the relief image may be post-exposed as in Examples V and XXIVor pre-exposed as in Example XXVI. Other variations may also be madewithin the scope of the claims.

The resin used in the following examples was a thermoplastic rubber-likepolymer described in U.S. Pat. No. 3,265,765. The material is a blockcopolymer of polystyrene and polybutadiene. In each formulation 10 gramsof the resin material in the form of dry pellets was employed. Thefollowing photosensitizers and crosslinking agents were added in theseformulations, each being given an example number.

    __________________________________________________________________________                 Example Number                                                   Additive.sup.1                                                                             XXVII                                                                             XXVIII                                                                             XXIX                                                                              XXX                                                                              XXXI                                                                              XXXII                                                                             XXXIII                                                                             XXXIV                                                                              XXXV                           __________________________________________________________________________    Photosensitizer:                                                              Benzoin          0.02 0.02.sup.1                                                                           0.10                                             Phenanthrenequinone       0.2                                                 Michler's ketone                 0.0007                                                                            0.007                                                                              0.014                                                                              0.14                           Crosslinking agent:                                                           Triallyl cyannurate                                                                        0.60                                                                              0.60     0.60                                                                             0.60         0.60 0.60                           Pentaerythritol triacrylate                                                                         0.60.sup.                                               Polyvinyl cinnamate.sup.2        0.013                                                                             0.333                                    __________________________________________________________________________     .sup.1 Numbers are in grams/10 grams of resin.                                .sup.2 Serves as photosensitizer as well as crosslinking agent.          

In making these formulations into photoresist sheets, the pelletmaterial was thoroughly dry mixed with the additives and then themixture was dissolved in about 50 cc of methylene chloride. Sufficientsolvent should be used to completely dissolve the resin. The amount ofsolvent above this indicated minimum is not critical; however, it ispreferred to use an amount approaching the minimum to reduce thequantity of solvent which must be subsequently removed and recovered.After the methylene chloride was removed by evaporation, the resultingcomposite material was comminuted into small pieces which were moldedinto sheets using a pressure of 25,000 psi and 225° F. For theseexamples, the sheet ranged in thickness between 0.039 and 0.045 inch.

Sheets of each of the nine formulations were contacted with aphotographic negative serving as the process transparency and exposed toultraviolet radiation from a 435-watt ultraviolet lamp (Hanovia LampDivision, Engelhard Hanovia, Inc.) for from about 4 to 128 minutes.Subsequent to this exposure the sheets were adhered to a glass surfacewith cement and then the unexposed nonprinting background areas werewashed out with xylene.

Of Examples XXVII-XXXI, Example XXVII containing no photosensitizer, didnot develop any perceptible printing surface; while Examples XXVIII andXXIX, with the smaller amounts of benzoin as photosensitizer wereobserved to have raised printing surfaces of the order of 5 to 10 mils.Examples XXXI had a perceptible printing surface but Example XXX, whichcontains 2% by weight of the photosensitizer, was not satisfactory, dueapparently to excessive light screening by the high content of thephotosensitizer.

Of Examples XXXII-XXXV, Examples XXXII and XXXIII gave the best printingsurfaces with raised indicia ranging between 0.010 to 0.013 inch high inExample XXXII, and between 0.016 to 0.025 inch in Example XXXIII.Example XXXIV had raised indicia of about 0.006 inch while Example XXXV,with a 10-fold increase in photosensitizer over Example XXXIV, had noperceptible indicia on the surface.

Generally, indicia heights between 0.015 and 0.040 inch are desirablefor good letterpress printing. However, the conditions of printing andthe number of impressions desired may determine this parameter.

EXAMPLE XXXVI

A photosensitive, thermoplastic composition is prepared as follows:

1.40 parts 2,2-dimethoxy-2-phenylacetophenone is dissolved in a mixtureof 5.30 parts hexamethylene glycol diacrylate, 3.70 parts hexamethyleneglycol dimethacrylate, 0.166 part 2,6-di-tertiary-butyl-para-cresol and0.001 part hydroquinone. A solution of C.I. 109 Red Dye (0.003 part) inhydroxyethyl methacrylate (0.13 part) is added to the mixture. Thissolution is added to 82.30 parts polystyrene-polyisoprene-polystyreneblock copolymer (Kraton®1107, Lot No. 06BBF, manufactured by ShellChemical Co., Polymers Division, Houston, Tex.) in a twin screwextruder. A mixture of 6.0 parts α-methyl styrene/vinyl toluene resin(softening point 100° C., refractive index 1.583, viscosity at 25° C.for a 65% solution in toluene is 1.6-1.9 poises, manufactured byHercules, Inc., Wilmington, DE), and 1.0 part grated microcrystallinehydrocarbon wax (melting point 73°-76° C., flash point 113° C.,manufactured by International Wax Refining Co., Valley Stream, N.Y.) ismelted at about 100° C. and is metered into the photosensitive mixturein the extruder. The twin screw extruder performs the function ofmelting, mixing, deaerating and filtering the photosensitivecomposition.

The following coating solution is prepared:

    ______________________________________                                        Ingredient           Amount (%)                                               ______________________________________                                        Methylene chloride   81.0                                                     Methanol             2.0                                                      N--methyl pyrolidone 10.0                                                     Polyamide resin, Lot No. 0B25005.sup.1                                                             7.0                                                      ______________________________________                                         .sup.1 The polyamide resin, Macromelt ® 6900, a product of Henkel         Adhesives Company, a division of Henkel Corporation, 4620 West 77th           Street, Minneapolis, MN is essentially colorless, has a Ball and Ring         Softening Point, of 266-302° F.; melt index at 347° F. of       5-15 g/10 minutes; flash point 570° F.; percent water absorption,      day is 0.2, 7 days is 0.5; tensile yield of 1,200 psi; tensile break of       3,500 psi; and elongation of 540%. The tensile yield, tensile break and       elongation are determined at 24° C. according to ASTM Procedure        D1708).                                                                  

The above polyamide resin coating solution is coated on 0.005 inch(0.127 mm) thick polyethylene terephthalate film using an extrusion diecoater to provide a dry film thickness of 0.00017 inch (0.004 mm) on thefilm, and the dry coated film is wound on wide stock cores.

The photosensitive composition described above is extruded at 160° C.through a die. The extruded composition enters the rotating bank in atwo-roll calender and is calendered between two films, one being a 0.005inch (0.127 mm) flame-treated polyethylene terephthalate support film,and the second being the polyamide-coated polyethylene terephthalatefilm described above (flame-treated and polyamide sides adjacent to theextruded photosensitive layer). The calender nip can be adjusted toproduce photosensitive layers over a wide range of thicknesses, e.g.,0.112 inch (˜2.85 mm) thick.

The photosensitive element having a photosensitive layer thickness of0.112 inch (˜2.85 mm) is cooled with blown air and is passed under abank of black light fluorescent tubes, such as Sylvania's BL lamps,placed transverse to the path of movement, continually exposing theelement through its support to polymerize a predetermined thickness ofthe photosensitive layer adjacent the support. The element is cut toconvenient lengths, e.g., 40 inches.

The photosensitive element is placed in an exposure unit, as describedbelow, and is given an overall exposure in air through the support for apredetermined length of time (for example, a 0.112-inch (182.85 mm)thick photosensitive layer requiring the polymerization of an 0.080 inch(2.03 mm) portion of the layer is exposed for about 3 minutes dependingon lamp intensity).

The polyethylene terephthalate film on the surface of the polyamidelayer is stripped therefrom. The polyamide layer remains adhered to thephotosensitive layer. The hard, flexible smooth polyamide surface iscovered with an image-bearing transparency, and the photosensitive layeris imagewise exposed for 5 minutes under vacuum in a Cyrel®3040 ExposureUnit (registered trademark of E. I. du Pont de Nemours and Company)fitted with Sylvania BL-VHO fluorescent lamps.

After exposure the transparency is removed, and the exposed element isplaced in a rotary drum-brush type Cyrel®3040 Processor. Theunpolymerized areas of the element are removed in the processor bywashing with a mixture of 75 volume percent tetrachloroethylene/25volume percent n-butanol. The developed element (printing plate) isplaced in a forced hot air drier or other suitable drier and is dried at60° C. until the plate attains its original thickness. The dry plate isthen detackified for 1 to 3 minutes in a solution of aqueous acidichypochlorite (900 parts water, 90 parts Clorox®, 10 parts conc. HCl).The wet plate is post-exposed in air for 10 minutes using the sameexposure source used for the imagewise exposure described above. Theplate has a Shore® A hardness in the range of 50-55.

The plate can now be mounted on a flexographic press cylinder withcommercially available double sided adhesive tape and printed withstandard flexographic inks. The print quality is equal to or better thanthat produced with rubber plates printed in the same manner.

What is claimed is:
 1. A process for forming a solvent-soluble,photosensitive elastomeric element comprising applying to a sheetsupport a layer of a photosensitive, elastomeric composition to a drythickness of from about 0.005 to about 0.25 inch, said compositioncomprising(1) at least 30% by weight of at least one solvent-soluble,thermoplastic, elastomeric block copolymer containing at least twothermoplastic, nonelastomeric polymer blocks having a glass transitiontemperature above 25° C. and an average molecular weight of2000-100,000, and between said thermoplastic, nonelastomeric polymerblocks an elastomeric polymer block having a glass transitiontemperature below 10° C. and an average molecular weight of about 25,000to 1,000,000, (2) at least 1% by weight of an addition-polymerizableethylenically unsaturated compound containing at least one terminalethylenical group, and (3) a polymerization-effective amount ofpolymerization initiator activatable by actinic radiation;laminatingonto said layer a combination of (a) a strippable flexible cover sheethaving coated thereon (b) a solvent-soluble, flexible, polymeric film,so that the surface of said film is contiguous to the surface of saidlayer.
 2. A process according to claim 1 wherein the photosensitive,elastomeric composition is applied to the sheet support by extruding atan elevated temperature.
 3. A process according to claim 1 wherein thephotosensitive, elastomeric composition is applied to the sheet supportby calendering.
 4. A process according to claim 3 wherein thephotosensitive, elastomeric composition is calendered between twosheets.